Gear pump

ABSTRACT

A gear pump includes at least one wear plate slidable in a bore in the pump casing towards and away from the pump gears parallel to the axes of the gears. Vacuum on the suction side of the pump draws the wear plate against the side face of the gears and a compression spring is provided to resist excessive pressure between abutting faces of the wear plate and the gears. A separate spring may be provided for each wear plate or one spring may act on two wear plates on opposite sides of the gears.

United States Patent [191 Turolla 1 Feb. 5, 1974 GEAR PUMP [76] Inventor: Marco Turolla, 213, Via Toscana,

Bologna, Italy [22] Filed: Nov. 5, 1971 [211 App]. No.: 195,928-

'[30] Foreign Application Priority Data Nov. 28, 1970 Italy 13056/70 Aug. 10, 1971 Italy 12860/71 [52] US. Cl. 418/131 [51] Int. Cl. F01c 19/08 [58] Field of Search 418/135, 132, 131

[56] References Cited UNITED STATES PATENTS Compton 418/132 3,104,616 9/1963 Peet 418/132 Primary ExaminerCarlton R. Croyle Assistant Examiner-Michael Koczo, Jr.

Attorney, Agent, or Firm-Berman, Bishoff and Platt 57 ABSTRACT A gear pump includes at least one wear plate slidable in a bore in the pump casing towards and away from the pump gears parallel to the axes of the gears. Vacuum on the suction side of the pump draws the wear plate against the side face of the gears and a compression spring is provided to resist excessive pressure between abutting faces of the wear plate and the gears. Aseparate spring may be provided for each wear plate or one spring may act on two wear plates on opposite sides of the gears.

. 12 Claims, 9 Drawing Figures PATENIED FEB 5 I974 SHEU 1 IF 4 INVENTOR UROLLA,

MARCO M, 1% W0 ATTORNEY,

PATENTEDFEB Sign sum u or" 4 INVENTOR T u A? 0 L LA,

5 BY 292 a a 7 Wag/70 ORNEYJ.

GEAR PUMP BACKGROUND OF THE INVENTION The invention relates to a gear pump in which on at least one side of the gears there is disposed a wear plate which fits closely into the pump casing bore, is movable in the axial direction is adapted to be pressed sealingly against the associated side of the gears, serves as sealing or bearing plate, and is provided with bores for the passage or for the mounting of the gear journals,

In the event of a breakdown in the operation of known gear pumps of this kind, for example the clogging of the suction pipe or of a filter provided in the latter, the vacuum on the suction side of the pump may reach so a high a value that the wear plate is drawn inwards, that is to say against the gears, by this vacuum, and is pressed with excessive force against the respective side surface of the gears. Not only does this prevent the gears from turning, but the wear on the cooperating side surfaces of the wear plate and the gears issubstantially increased. Furthermore, as the wear plate is subjected to the action of the increased vacuum eccentrically, that is to say only in its region adjacent the suction side of the gear pump, this may result in irregular wear or tilting and consequent jamming of the wear plate in the pump casing bore. Tilting of the wear plate also lifts the plate slightlyoffthe side surface of the gears on the delivery side of the pump. This lifting leads to cavitation or vibration phenomena, which give rise to erosion of the cooperating side surfaces of the wear plate and the gears.

The invention is concerned with eliminating these disadvantages of known arrangements and providing a gear pump of the type first mentioned above, in which with simple and inexpensive technical 'means it is possible to avoid excessive pressure of the wear plate against the side surface of the gears, and the corresponding obstruction of the rotational movement of the gears or intensive, irregular wear on the-abutting surfaces of the wear plate and of the gears, aswell as tilting'or jamming of the wear plate and damage to the gear pump through the action of increased vacuum on the suction side of the pump.

SUMMARY The present invention provides a gear pump comprising a pump casing, engaging gear members rotatable within the casing, a bore within the casing extending parallel to the axes of the gear members, and a wear plate fitting closely within said bore on at least one side of the gears, the wear plate being movable in the axial direction and adapted to be pressed sealingly against the associated side surface of the gears, bores being provided in the wear plate for receiving the gear journals, resilient repelling means being disposed on the suction side of the pump and arranged to press the wear plate outwards away from the gears, the repelling means having spring characteristics which limit increase of pressure between the wear plate and the side surface of the gears.

In this arrangement the wear plate is pressed against the respective side surface of the gears against the force of resilient repelling means. The spring characteristics of the repelling means are so selected that under normal operating conditions, that is to say with normal vacuum on the suction side of the pump, the wear plate is drawn inwards by the vacuum and is permitted by the repelling means to be pressed uniformly and sealingly against the side surface of the gears. When the vacuum on the suction side of the pump is increased excessively, or when a determined value of this vacuum is exceeded, for example as the result of the clogging of the suction pipe connected to the gear pump, the resistance offered by the resilient repelling means nevertheless becomesso great that any further increase of the pressure urging the wear plate against the associated side surface of the gears beyond a determined maximum permissible value is reduced. The high or very high vacuums on the suction side of the pump are consequently unable to obstruct the rotational movement of the gears and also unable to increase beyond a predetermined value the wear on the cooperating side surfaces of the wear plate and gears. Since in addition the resilient repelling means are-disposed'in the region of the suction side of the gear pump, that is to say in the portion of the wear plate which is subjected to the vacuum, they also prevent thewear plate from tilting or becoming jammed under the action of the particularly high vacuum. Consequently uniform wear of the wear plate is ensured and the plate is prevented from being lifted off the side surface .of the gears on the delivery side of the pump so that the cavitation or vibration phenomena caused thereby cannot occur.

ln'a convenient embodiment of the invention the resilient repelling means consist of at least one compression spring. This spring may be clamped between the wear plate and the pump casing. In this case his particularly advantageous for the expanding spring to be in the form of asteel wire spring bent approximately into Z-shape and which acts with one arm on the pump casing and with the other arm on the wear plate. In the case of gear pumps having wear plates disposed on both sides of the gears, each wear plate may be provided with at least one separate spring clamped between the pump casing and the respective wear plate. A particularly simple embodiment is however obtained in gear pumps having wear plates disposedon both sides of the gears by clamping at least one expanding spring between the two .wear plates. In this case it is advantag'eous for this expanding spring to be in 'the form of a steel wire spring bent approximately into U-shape and acting by one arm against'one wear plate and by the other arm against the other wear plate.

It is preferable for the Z-shaped or U-shaped expanding springs to be in the form of double one-piece steel wire springs which are disposed symmetrically about the centre plane of the, pump extending through the suction passage of the pump casing and parallel to the axes of the gears. In this case the two portions of the steel springs which extend parallelto one another may be connected to one another only at one end or at both ends of the arms of the spring. In the former case the ends of the two portions of the wire spring may terminate at the open end of the spring anns in the form of straight fork prongs parallel to one another, or may be bent over inwards towards one another.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a gear pump embodying the invention with wear plates which are disposed on both sides of the gears and are in the form of bearing plates for the gear journals and each of which is pressed outwards by a Z-shaped expanding spring, this figure being a crosssection and showing the gear pump in the completely assembled state;

FIG. 2 shows the gear pump of FIG. 1 with the pump casing covers removed;

FIG. 3 is a section on the line IIIIII in FIG. 1;

FIG. 4 illustrates in perspective an expanding spring used in accordance with FIGS. 1 to 3;

FIG. 5 shows in cross-section and in the completely assembled state a gear-pump embodying the invention having wear plates which are disposed on both sides of the gears and are in the form of bearing plates for the gear journals and which are pressed outwards by a common expanding spring;

FIG. 6 shows the gear pump of FIG. 5 with the pump casing covers removed;

FIG. 7 is a section on the line VII-VII in FIG. 5;

FIG. 8 shows in perspective the expanding spring v used in the pump according to FIGS. 5 to 7;

FIG. 9 shows a cross-section in the completely assembled condition of a gear pump embodying the invention with wear plates which are disposed on both sides of the gears and are in the form of sealing plates and which are pressed outwards by expanding springs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS covers 5, 6 are joined to the pump casing 1 by bolts (not illustrated) which are parallel to the axes of the gears 2 and pass through corresponding bores 7.

On each side of the gears 2 there is disposed in the pump casing 1 a wear plate 8, which is an exact fit in the bore 101 of the pump casing land is slidable' therein in the axial direction. The bore 101 of the pump casing 1 and the wear plates 8 have approximately the shape of a figure of eight, as can be seen particularly in FIG. 3. In the example illustrated in FIGS. 1 to 3 the wear plates 8 are in the form of bearing plates for the gear journalsand consequently have bores in which the journals 102 of the gears 2 are mounted rotatably. One journal 102 of one gear 2 passes out of the pump casing through one wear plate 8 and the respective cover 6 and is adapted to be connected to a drive shaft (not shown). Each wear plate 8 is provided on the suction side of the pump with a recessed edge 9 disposed symmetrically to the centre plane M of the pump, which extends through the suction port 3 and isparallel to the gear journals 102, as can be seen particularly in FIG. 3. In this recessed edge 9 is disposed a Z-shaped expanding spring '10, which acts by one art 110 on the pump casing l and by its other arm 210 on the respective wear plate 8, pressing the latter outwards, that is axially away from the gears 2. The expanding spring 10 is in the form of a double one-piece steel wire spring bent into Z-shape, as can be seen particularly in FIG. 4. The ends of the two mutually parallel portions of this Z-shaped steel wire springs 10 are joined together only at the spring arm 210 which abuts the wear plate 8. This arm 210 of the Z-shaped steel wire spring 10 engages in a recess 11 which is provided in the side surface of the wear plate 8, facing the gears 2. At the end of the other arm 110 of the Z-shaped steel wire spring 10, the two mutually parallel portions of this spring which act on the pump casing 1, are not joined together. This arm of the steel wire spring 10 consequently has a fork-like shape and the corresponding free ends of the two portions of the spring engage in respective bores provided in the pump casing l, as can be seen particularly in FIGS. 1 and 2. The two portions of the double Z-shaped steel wire spring 10 lie symmetrically on opposite sides of the centre plane M extending through the suction port 3 of the pump.

The two wear plates 8 are pressed in use of the pump against the respective side surfaces ofv the gears 2 against the repelling force of the respective expanding springs 10 disposed on the suction side of the pump. This can for example be seen through the fact that when the covers 5, 6 of the pump casing 1 are removed the wear plates 8 move away from the gears 2 under the action of the expanding spring 10, that is to say are pressed outwards, and protrude slightly from the pump casing 1, as can be seen in particular in FIG. 2. The spring characteristics of the expanding springs 10 are so selected that under normal operating conditions,

that is to say with normal vacuum in the suction port 3 of the pump, these springs allow the wear plates 8, which are drawn inwards by the vacuum, to achieve the necessary unifonn sealing pressure of the wear plates 8 against theassociated side surfaces of the gears. If the vacuum in the suction port 3 of the pump is increased excessively, that is to say when this vacuum reaches a predetermined value, for example through the clogging of the suction pipe (not illustrated) connected to the suction port 3, the resistance offered by the expanding springs 8 however becomes so great that it prevents excessive pressure between the wear plates 8 and the side surfaces of the gears 2.

The gear pump illustrated in FIGS. 5 to 7 corresponds to that shown in FIGS. 1 to 3, and like parts are given the same reference numerals. While in the example illustrated in FIGS. 1 to 3 the wear plates 8 are each pressed outwards by a separate Z-shaped expanding spring 10, in the example illustrated in FIGS. 5 to 8 a single expanding spring 12 is provided which is common to both wear plates 8 and which is clamped between the two wear plates 8 and simultaneously presses both plates in the outward direction. This expanding spring 12 is approximately U-shaped and is disposed in the recesses 9, which are provided in the edges of the wear plates 8 and are in alignment with one another, on the suction side of the pump. The two anns 112 of the U-shaped expanding spring 12 engage in the recesses 11, which are provided in the side surfaces of the wear plates 8 facing the gears 2. In this case also the U- shaped expanding spring 12 is in the form of a double U-shaped steel wire spring, as illustrated in FIG. 8. The two mutually parallel portions of this U-shaped steel wire spring 12 are joined together at the end of one arm 112 of the spring, while at the end of the other arm 112 they are bent inwards towardsone another but not joined. In addition, the recesses 9 provided in the edges of the two wear plates 8 on the suction side of the pump, are symmetrical with respect to the centre plane M of the pump, which extends through the suction port 3 of the pump casing land isparallel to the gear journals 102. In this way the twoportions of the double U- shaped steel wire spring 12 lie on opposite sides of and likewise symmetrically to the aforesaid centre plane M, as illustrated in FIG. 7. The two arms 112 of the U- shaped expanding spring 12 are preferably slightly inclined outwards in the unloaded condition, as illustrated in FIG. 6 in-which the pump casing covers 5, 6 are removed and the wear plates 8 consequently project slightly out of the casing 1.

In the examples illustrated in FIGS. 1 to 3 and 5 to 7 the wear plates 8 are also provided with edge recesses 9 and recesses 11 on their inner sides on the delivery side of the pump, although no expanding springs 10 or 12 are provided on this side of the pump. The provision on both sides of the edge recesses 9 and of the recesses 11 on the inner side has the sole purpose of manufacturing a single type of wear plate 8, so that by simply turning the latter through 180 the plate can selectively be used for both side surfaces of the gears 2. FIG. 9 illustrates a gear pump in which the wear plates 8 disposed on both sides of the gears 2 are in the form of sealing plates which have bores 108 for the passage of the gear journals 102. The journals 102 of the gears 2 are mounted rotatably in the covers 5 and 6 of the pump casing l by means of rolling contact bearings 13. In this construction of the pump the wear plates 8 are also pressed outwards by Z-shaped expanding springs 10 disposed on the suction side of the pump, as in the example illustrated in FIGS. 1 to 4. The Z-shaped expanding springs 10 associated with each wear plate 8 may in this case be replaced by a single U-shaped expanding spring 12 common to both the wear plates, as in the example illustrated in FIGS. 5 to 8.

The invention is not restricted to the examples illustrated. For example, other elastic or spring devices may be provided to act on the wear plate. The expanding springs may be in the form of leaf springs or one-piece steel wire springs of any shape.

I claim:

l. A gear pump comprising a pump casing, engaging gear members rotatable within the casing, a bore within the casing extending parallel to the axis of the gear members, and a wear plate fitted closely within said bore on one side of the gears, said wear plate being movable in the axial direction, means axially holding said wear plate against the associated side surfaces of the gears, bores in said wear plate for receiving the gear journals, resilient repelling means disposed on thesuction side of the pump and pressing said wear plate outwards away from the gears while permitting the wear plate to be drawn by normal negative pressure into sealing relation with said side surfaces of the gears against the action of said resilient repelling means, said repelling means having spring characteristics which opposes increase of pressure between the wear plate and the side surfaces of the gears, particularly upon uneven wear or twisting of the wear plate.

2. A gear pump according to claim 1, in which the repelling means consist of at least one compression spring.

3. A gear pump according to claim 2, in which the spring is clamped between the wear plate and the pump casing.

4. A gear pump according to claim 3, in which the spring is a steel wire spring bent approximately into Z- shape and which actsby one arm on the pump casing and by the other arm on the wear plate.

5. A gear pump according to claim 3,. with wear plates disposed on both sides of the gears, in which each wear plate is provided with at least one separate spring clamped between the pump casing and the respective wear plate.

6. A gear pump according to claim 1 having wear plates disposed on both sides of the gears, and in which at least one spring is clamped between the two wear plates.

7. A gear pump according to claim 6, in which the spring is in the form of a steel wire spring bent approximately in U-shape and each of the arms of which acts on a wear plate.

8. A gear pump according to claim 2, in which the springs are in the form of double one-piece steel wire springs and are disposed symmetrically about the centre plane of the pump which extends through the suction port of the pump casing and parallel to the gear journals.

9. A gear pump according to claim 8, in which two mutually parallel portions of the double steel wire spring are joined together only at the end of one arm of the spring, while at the other, open end of the spring arm they terminate in the form of straight fork prongs parallel to one another.

10. A gear pump according to claim 2, in which the spring is disposed in a recess provided in the edge of the wear plate or wear plates on the suction side of the pump.

11. A gear pump according to claim 7, in which the U-shaped spring is formed of double steel wirehaving a connected and closed end and an open end of which two mutually parallel portions of the double steel wire spring are bent over inwards. toward one another at the open end of the spring arms.

12. A gear pump according to claim 5, wherein each wear plate is provided along opposite edges thereof with diametrically opposite recesses so that it can be used selectively on either side of the gears, said recesses being adapted to receive said compression springs. 

1. A gear pump comprising a pump casing, engaging gear members rotatable within the casing, a bore within the casing extending parallel to the axis of the gear members, and a wear plate fitted closely within said bore on one side of the gears, said wear plate being movable in the axial direction, means axially holding said wear plate against the associated side surfaces of the gears, bores in said wear plate for receiving the gear journals, resilient repelling means disposed on the suction side of the pump and pressing said wear plate outwards away from the gears while permitting the wear plate to be drawn by normal negative pressure into sealing relation with said side surfaces of the gears against the action of said resilient repelling means, said repelling means having spring characteristics which opposes increase of pressure between the wear plate and the side surfaces of the gears, particularly upon uneven wear or twisting of the wear plate.
 2. A gear pump according to claim 1, in which the repelling means consist of at least one compression spring.
 3. A gear pump according to claim 2, in which the spring is clamped between the wear plate and the pump casing.
 4. A gear pump according to claim 3, in which the spring is a steel wire spring bent approximately into Z-shape and which acts by one arm on the pump casing and by the other arm on the wear plate.
 5. A gear pump according to claim 3, with wear plates disposed on both sides of the gears, in which each wear plate is provided with at least one separate spring clamped between the pump casing and the respective wear plate.
 6. A gear pump according to claim 1 having wear plates disposed on both sides of the gears, and in which at least one spring is clamped between the two wear plates.
 7. A gear pump according to claim 6, in which the spring is in the form of a steel wire spring bent approximately in U-shape and each of the arms of which acts on a wear plate.
 8. A gear pump according to claim 2, in which the springs are in the form of double one-piece steel wire springs and are disposed symmetrically about the centre plane of the pump which extends through the suction port of the pump casing and parallel to the gear journals.
 9. A gear pump according to claim 8, in which two mutually parallel portions of the double steel wire spring are joined together only at the end of one arm of the spring, while at the other, open end of the spring arm they terminate in the form of straight fork prongs parallel to one another.
 10. A gear pump according to claim 2, in which the spring is disposed in a recess provided in the edge of the wear plate or wear plates on the suction side of the pump.
 11. A gear pump according to claim 7, in which the U-shaped spring is formed of double steel wire having a connected and closed end and an open end of which two mutually parallel portions of the double steel wire spring are bent over inwards toward one another at the open end of the spring arms.
 12. A gear pump according to claim 5, wherein each wear plate is provided along opposite edges thereof with diametrically opposite recesses so that it can be used selectively on either side of the gears, said recesses being adapted to receive said compression springs. 